Which oil drain tube is leaking?
 

I have a small leak coming from the area where the turbo drain tube and air cleaner oil tube enter the lower oil pan. After cleaning the area and driving about 75 miles I noticed that the darkest spot is in between the two tubes, making me suspect that the leak could be coming from the smaller air cleaner tube. Does this mean that there is a check valve in the engine that could be failing or is it just a matter of replacing that o-ring down there on the nipple? Thanks

Replace the o-ring and watch it again.

X2 on replacing the O-Ring but replace the O- ring on the upper end also so Oil does not leak there and run down the side of the Tube.

If it turns out the Valve at the Air Filter to Crankcase Drain is the issue there is some threads on how others have cleaned theirs without removing it or dropping the pan.